a lot of possible cause, might be a clock issue, overheat, risers, Power supplies, etc
Are your GPU's modded?
Start with a default command lines and default clocks excluding those above
check also your miner logs and windows logs thru event viewer
you may get a hint what would be the cause
in windows type eventvwr\windows Logs\Application
Yes, My gpu is modded
im check windows logs
i found some errors there
from System
The computer has rebooted from a bugcheck. The bugcheck was: 0x000000ea (0xffff90854aa3f080, 0x0000000000000000, 0x0000000000000000, 0x0000000000000000). A dump was saved in: C:\Windows\MEMORY.DMP. Report Id: 585eea90-3d66-4476-9908-2e491f4e08f6.
The previous system shutdown at 17:48:19 on 10/08/2018 was unexpected.